Benzimidazoles are known to be useful in combating intestinal parasites of mammals and birds. Furthermore, 2-trifluoromethylbenzimidazoles have been found to be useful as herbicides, nematocides, molluskicides, and insecticides. [British Pat. No. 1,087,561; U.S. Pat. No. 3,412,101; South African Pat. No. 65/5584; Netherlands Pat. No. 67,13786; (Derwent Basic No. H2118) are exemplary.] The 2-trifluoromethyl derivatives most frequently employed as insecticides have been substituted in the benzene portion of the benzimidazole ring system with chlorine and nitro groups, with the most active compounds being 2-trifluoromethyl-4,5,6,7-tetrachlorobenzimidazole, 2-trifluoromethyl-5,6-dichlorobenzimidazole, and phenol 2-trifluoromethyl-4-nitro-6-chloro-1-benzimidazolecarboxylate. In general these compounds have shown their greatest activity against insects of the order Lepidoptera, such as Southern armyworm, and of the order Diptera, such as house flies and mosquitoes. For example, 2-trifluoromethyl-4,5-dichlorobenzimidazole gives a complete kill of Southern armyworm larvae at 250 ppm, but is without action against milkweed bugs, oriental roaches and boll weevils at that same concentration, and in fact, its activity against house flies is excellent only at 1000 ppm. The isomeric compound, 2-trifluoromethyl-5,6-dichlorobenzimidazole, has the same excellent activity against Southern armyworm larvae at 250 ppm, but no activity at the same level against milkweed bugs, house flies, oriental roach and boll weevil. In general, these chlorinated benzimidazoles do not approach, in absolute activity, the organic phosphate insecticides, nor do they have the same broad spectrum of action.
Two large classes of marketed insecticides which have been widely used and which have a reasonably broad spectrum against many orders of insects plus a low dosage range are the organic phosphates and the chlorinated hydrocarbons. Many of the most active of the organic phosphate insecticides are extremely toxic to humans and their toxicity by intradermal absorption is of the same order of magnitude as their toxicity by inhalation. Thus, these very toxic compounds are extremely dangerous to handle, even when using a gas mask or oxygen mask. The safest of the phosphorous insecticides, malathion, is still widely used, but its spectrum is not as broad as would be desirable and many species of insects or mites have become resistant to it over the years.
The deficiencies of the chlorinated hydrocarbons are of a different nature. Resistance is, of course, prevalent, but this problem is not as serious as might be expected because of the endless succession of new chlorinated hydrocarbons which have beend produced. The chief drawback to the use of chlorinated hydrocarbons is their persistance in soil and water for many, many years, attributed chiefly to their metabolic stability. This persistance has now begun to affect other forms of life, including birds and fish.
Thus, there is a need for compounds with both insecticide and miticide activity, which have a broad spectrum, are safe to handle and are non-persistant.